This invention is concerned generally with the measurement of the spatial distribution of radiant energy such as that of reradiated light produced by scattering and fluorescence. More particularly the invention is concerned with the measurement of the energy and direction of light flux or rays produced and reradiated or distributed by particles passing through an optical sensing zone whereby to enable the identification of the particles and/or their characteristics.
One problem with known measurement systems (not including those which are disclosed in the said copending applications) is that they are limited considerably in the range of polar angles that can be measured. For the purposes of this discussion the optical axis of reradiation may be considered the line of the incident light beam projected at a sensing zone where a particle intersects the same. Using conventional definitions, the polar angles are those defined by the angles of the optical axis with lines centered at the sensing zone or point and radiating from that zone, while the azimuthal angles are those measured around the optical axis.
One attempt has been made to evolve an arrangement which can measure multiple angles by means of an integral, planar, geometric configuration of photovoltaic detectors, but the problem with this device is that it can only measure polar reradiating angles from about 1.degree. to somewhat less than 25.degree.. Any attempt to measure the energy distribution in most polar angles in the forward (0.degree. to 90.degree.) and all angles in the backward direction relative to the sensing or scattering zone and the incident light direction including all azimuthal angles, fails because the sensitive area of the device is too small. This is because all of the photovoltaic elements which "see" the energy must be mounted on the same plane within the available space which is limited. Accordingly the utility of the device is limited.
The particular device which is referred to is in the form of a concentric ring and wedge photovoltaic detector. It is described in considerable detail in U.S. Pat. No. 4,070,113 and in two articles entitled "Light-Scattering Patterns of Isolated Oligodendroglia" by R. A. Meyer, et al in The Journal of Histochemistry and Cytochemistry, Vol. 22, No. 7, pp 594-597, 1974 and a second article entitled "Gynecological Specimen Analysis by Multiangle Light Scattering in a Flow System" by G. C. Salzman et al in the same journal, Vol. 24, No. 1, pp 308-314, 1976. In these articles reference is made to the same or a similar detector device which is commercially available and which is identified as a Recognition Systems, Inc. detector (RSI).
The configuration of detectors which has been mentioned above will be referred to hereinafter as a planar configuration of detectors. As known at this time the one mentioned in the above references is expensive, difficult to manufacture, delicate, inefficient and slow-acting because of its relatively large area considering the number of detectors which it carries. The inefficient optical design results in a poor signal to noise ratio.
Notwithstanding these disadvantages, such a configuration and in general any radiant-to-electrical energy transducers configured in a geometric assemblage which is planar are and can be useful within the field they occupy, but according to the invention herein, this usefulness is materially increased. The planar configuration of detectors at the minimum can serve the purpose of helping to find a location at which some desired set of polar reradiating angles are the optimum for a given optical system and for a particular family or type of particles being studied.
Once an optimum position has been achieved in a given system, the planar configuration of photovoltaic detectors may be removed from the system and a more economical device substituted therefor, this latter device comprising a composite deviating lens or reflector which is formed of a large number of elements such as prisms each oriented to deviate or reflect a certain geometric portion of the reradiated energy area being studied to different and spaced apart commonly available and highly economical photodetecting devices such as small photocells. The measurements from all of the photocells give the information desired.
Prior art patents which may be of interest are: U.K. Pat. No. 137,637 of 1920 to Pollard and Frommer U.S. Pat. No. 3,248,551.